Full-wave rectifier tube



April 25, 1950 c. N. SMYTH FULL-WAVE RECTIFIER TUBE 2 ,Sheet s+Sheet Filed Jan. 20, 1946 2 we a INVENTOR 67/144263 M S/VYT/v BY ATTOR EY April 25, 1950' c. N. SMYTH FULL-WAVE 'REC'IIFIER TUBE 2 Sheets-Sheet 2 Filed Jan. 20, 1945 INVENTOR Ca /4191A? M SMYTH ATTORNE-Y Patented Apr. 25, 1950 FULL-WAVE RECTIFIER.- TUBE Charles Norman Smyth, London, England, as-

signor, by mesne assignments, to International Standard Electric: Corporation, New York, N; Y'., a. corporation of Delaware Application January 20, 1945., Serial No. 573,774. In Great; Britain February 7", .1944

11 Claims. 1.

The present invention relates to thermionic rectifiers; and, rectifying; circuits ofthe full wave type and concerns particularly but not exclusively,, a valve design suitable for miniaturerectlfiers, or for other cases where the anode dissipation is relatively large.

A full wave rectifier comprising two diodes assembled in the same envelope is well known, and both. cathodes are usually operated atthe same potent-lab quite commonly a single cathode servcs iorboth the diodes, two separate anodes being: provided. In the conventional rectifying circuit the anodes are; at high A. C. potentials in oppositephase,, and the cathodes are usually at a positive potential. it istherefore necessary to insulate the cathode heating circuit to-stand up to any voltages likely to occur between the cathodes and earth, and this is cloneeither by suitably insulating the heaters themselves from the; cathodes or; by supplying them from a. suitably insulated source such as aninsulated transformer winding, or by bothmethods.

Power rectiflers or this type have considerable anode dissipation, and radiating fins are often provided on the anodes inside the envelopeto keep them at a reasonable temperature during operation. In cases where space is a consideration, it has been found diflieult to reduce the size of these rectifiers sufiieiently on account of the bulky nature of the cooling arrangements;

Hall wave rectifiers have of course been made in which the anode is part of the envelope; enabling external coolingmeans to be applied, but asin the conventional arrangements the anode is operated at a high A. 6; potential, an external anode has obvious disadvantages. The provision of two such. high potential external anodesffor a. full wave rectifier presents considerable diniculties.

It: has; been found; that. all: these; troubles may e; avoided; and full. wave rectifiers or smalli dimensions. man be:- eonstructedj by designates: the rectifier with: a anode; but withseparate cathodes, and bym difyin tha cireuirarran emcnts so. that; the; common an de. is. operated. at around; potential. The: common. anode than preferably calamar osa metal; disc sealed throughv the; envelope-o1? hereoiinerrvalva to which disc may? e nte ral y attached; extension platesor the like. loseto. he. cathodes tel-arm. the. anode V one. anoiihen. thee arrangement. being. for

xample... on;- similar lines to; the: disc. sear anode val e; described; in. he specification or: the: cm

2 pending application, Seri uar-y II, 1945.

The invention accordingly provides a thermionic valve rectifier comprising an envelope, a plurality of electron emissive cathodes insulated from one. another enclosed in the:- said envelope, and a single anode common to. all the said cathodes.

The invention also provides an electrical circuit arrangement for rectifying; a multi-phase alternating voltage comprising athermionie valve rectifier having a. plurality of insulated electron emissive. cathodes corresponding respectively to the phases and an anode common to all the said cathodes, means for applying between each cathode and a neutral point, an: alternating voltage in the phase corresponding to that cathode, and means. for connecting av direct current load between the. said anode and the said neutral-I point.

The invention will be described with reference to the. accompanying drawings, in- Which- Figs. 1 and 2 show schematic diagrams'of two rectifying circuits accordingto the: invention;

Fig; 3 shows aside view of a. thermionic valve rectifier according; to the invention;

Fig. 4 shows a. plan view of the anode disc. of Fig. 3;

Figs. 5. and 6 show modifications of the valve according. to. Fig; 3;

Fig. 7 shows. a preferred terminal arrangement for-thevalve; and

Fig. 8 shows a valve similar to Fig. 3 provided with a. metal can.

Fig. 1 shows a schematic circuit: diagram of a full wave rectifying arrangement according to diagrammatically and is not necessarily arranged with the cathodes on opposite sides of the anode. A power transformer-T has a primary winding P connected to a single phase-source of alternating current as indicated, and a centre-tapped secondary winding: So having its extreme. terminals connected respectively to. the cathodes C1. and C2. Two. additionalsecondary windings; S1; and S2 arerespectively' connected tothe heaters. H1 and" H2. The rectified. voltage is. obtained from the.- terminals I and 2 connected respectively to the. anode. A and to; the; centre. tap of the winding Sc. Terminal i will be the negative terminal and should preferably be connected to earth, as shown, so that theanode A will be. at: ground potential. Suitable smoothing filters (notshown) may be connected between the terminals 1. 2 and the load according to the usual practice.

It will be seen that in this arrangement the cathode potential can rise to a value equal to the sum of the A. C. and D. C. potentials. The oathodes must therefore be very well insulated from earth. As it is often difficult to provide insulation between the cathodes and their respective heaters which will stand up to such high voltage, each heater is preferably supplied with current from a separate transformer winding appropriately insulated. This would permit each cathode to be connected to its heater, and would also allow directly heated cathodes to be used. If, however, the heaters are satisfactorily insulated from their respective cathodes, then they could be both heated from a single transformer winding, either in series or in parallel, or from some other source not necessarily insulated from ground.

It is to be noted that means should preferably be provided'to prevent direct communication of electrons from one cathode to the other. One way of doing this is to place the cathodes on onposite sides of the anode in the manner diagrammatically shown in Fig. l. to interpose an extension of the anode between the two'cathodes to act in the manner of a screen, or to enclose the cathodes in separate metal tubes or boxes connected together or attached to a common metal plate. Still another expedient is to remove the actiyating material from adjacent surfaces of the two cathodes so that neither emits electrons on the side facing the other.

Exactly the same principles are applicable to a multiphase rectifier. A separate cathode is provided for each of the phases concerned and all share a common anode. Fig. 2 shows how the circuit could be arranged in the case of a threephase rectifier. single anode A and three separate cathodes C1, C2 and G3 with corresponding insulated heaters H1, H2 and H3. Only the three secondary windings W1, W2 and W3 of the three-phase transformer connected to a three-phase supply are shown, and they are arranged in star formation with the points of the star connected respectively to C1, C2 and C3.' The terminals I, '2 for the rectified voltage are connected respectively to the :anode A and to the common point of the three secondary windings, and terminal i is preferably connected to ground, as shown. The three heaters H1, H2 and He. may be connected to corresponding extra insulated secondary windings (not shown) of the three-phase transformer, or if suitably insulated they may be all supplied from a common winding or other common source. To prevent direct transfer of electrons between the cathodes, extension plates such as are indicated at A1 and A2 may be attached to the anode A to screen each cathode from its neighbour.

ranged in a similar way. The output secondary windings corresponding to the phases will be connected to a common point which is connected to the positive output terminal, and the remaining terminals of these windings will be connected respectively to a corresponding number of cathodes provided in the valve V, the common anode of .which is connected to the negative output terminal,

and is preferably also connected to round. I

Another way is The rectifying valve V has a Fig. 3 shows a preferred form of construction for a rectifying valve having two cathodes, and suitable for use in the circuit of Fig. 1. To the upper side of a disc I i of copper or other suitable metal is sealed a glass dome l2, and to the lower side of the disc is likewise sealed a glass cup 13 having a glass disc base I4 carrying a number of terminal pins or rods [5 sealed therethrough.

Mounted on the terminals as indicated by means of the wires l6 and l! (or in any other convenient way) is an assembly comprising two mica sheets I8 and 19 holding the two cathodes 20 and 2| having corresponding heaters (indicated by the dotted lines) fixed therein in any suitable way. The cathodes and heaters are connected by suitable wires to corresponding terminals i5 as indicated.

Anode extension plates 22, 23 and 2 3 are soldered or spot-welded or otherwise rigidly attached to the disc H, and are located in slots in the mica sheets l8 and I9. The view of the underside of disc H seen in Fig. 4 indicates how these plates appear in plan. A getter holder 25 is located inside the dome l2 (Fig. 3) and is secured to the disc H. The valve is finally exhausted and sealed off at the tip 26.

The valve may be constructed in substantially the same way as those described in the co-pending application previously referred to. Thus the disc ll with the plates 22, 23 and 26 already attached is first sealed to the dome l2, and the getter holder 25 is inserted through the slot 2! (seen in Fig. 4) providedfor the purpose in the disc, and is soldered into the small hole 28. The cathode assembly is mounted in the cup l3, and the two parts are then brought together so that the anode extension plates enter the corresponding locating slots in the mica sheets l8 and [9. The seal between the cup l3 and the disc I! is finally made. The valve may then be outgassed and exhausted and the getter fired, and afterwards it may be sealed off at the tip 28.

Fig. 5 shows in section a variation in which two anode extension plates attached to the disc H are provided, the section being taken roughly half way between the two mica sheets if; and 19 in Fig. 3. The two cathodes 20 and 2! are placed side-by-side between the two anode plates 29 and 3B,,and a screening partition 3| connected to the anode plates is placed between them. The mica sheets 18, and 19 will, of course, be provided with locating slots appropriate for the modified form of the anode extension plates.

If the mutually adjacent surfaces of the cathodes 20 and 2| are not coated with emissive material, the screening partition 3! could be omitted if desired. This partition also need not be integral with the anode disc or plates, but it is desirable to connect it thereto.

In the arrangements described with reference to Fig. 3 or 4, the leakage path between the oathodes and the anode may be rather short, and to avoid this the anode extension plates may be shaped in reentrant form. Thus Fig. 6 shows, for example, how the plates of Fig. 5 may be arranged. Fig. 6 is a side view of the assembly as it would be seen from the right hand side of Fig. 5. Owing to the form of the plates 29 and 30 they preferably constitute part of the lower assembly, and are placed in position in-the mica sheets before the two parts of the valve are brought together for final sealing. The upper ends of theseplates are'provided with suitable tongues which enter locating slots at 32 and 33 inthe disc ll, being soldered in place during the 5: final processing'of'the.valva The partition 3| could. be. initially attachedtothe disc Li or'tothe plates 29 and at as may be most, convenient, but should be long enpugl to screen cathodes from one another overtheir whole length. Relatively wide clearance slots for the partition 3i should; be: left. in. the mica; sheets; t3 and? is; so. as tmavoid shortening the. iealzage-- path. Sincein theicasezof Fignfi themica sheetswill probablybe morenearly: square in. shape, it may be: desirable to. provide four. supporting... wiresat the corners, and. twocof: thesewires.areindica-ted at t iz'andz sii.

The structure which. hasbeen described-1 with referencestio Figs. 3 to. 5. is; particularly suitable for: miniature. rectifying. valves; and for: such valves a standard glass disc base it is available, having seven pin terminals. This base is shown in plan in Fig. 7 where the seven pin terminals are marked with the same letters a to or shown in Fig. 3.

The connections of the two cathodes and their heaters should preferably be as indicated in Figs. 3 and 7. Terminal (1 is left blank, and this arrangement provides the best separation for terminals with a large potential difference between them.

According to the usual practice when disc terminals are used, the anode disc I I will preferably be clamped or sandwiched between two relatively heavy metal rings or plates making very good thermal contact, so that very rapid transfer of heat from the anode is obtained. In this way a very small rectifying valve may be provided while at the same time dissipating a large quantity of heat. rings or plates may be part of a metal can 36 enclosing the valve, and radiating fins 3! may be provided on the outside of the can if desired. The can may be connected to the unused pin :1

of the base, or it may be provided with a central peg and key 38 as indicated in Fig. 8 for connecting to a corresponding socket which may be connected to ground for earthing the can. If it should be desired to insulate the anode electrically from the can, the disc ll could be electrically connected inside the valve to the pin 11, and thin sheets of mica 39 and 40 could be interposed between the disc and the clamping rings or plates. This would provide the desired electrical insulation while still giving good thermal transfer from g the disc to the can.

As explained in the co-pending specification referred to above, it is particularly advantageous to assemble the getter holder 25 in the upper compartment of the valve since it will be well screened from the cathodes by the disc, and there will accordingly be no danger of contaminating the cathodes with the getter material. However, if desired the getter could be suitably arranged in the lower part of the cup l3, and if the disc H be composed of a metal (such as one of the cobalt-nickel-iron alloys) which is suitable for scaling to glass on one side only, the dome l2 could be omitted altogether, so that the disc ll would then form the closing means for the en As shown in Fig. 8 the metal clamping sion of? the arrangements which have. been de! sorihedq for, the case? when; there are, only two cathodes.

Although for. thelrea'sons given the form of: the valve-with the anodedisc sealed. to theenvelope is preferred, itneedmotbe, constructed. in this way; so long as a common anode is provided for all;- the. separate, cathodes. By the term. com.- mon anqde is meant either an integral unit or single electrode shared by. all the cathodes, or a numben of anodeswhich may be structurally sen.- a-rate, butwhich are electrically. bonded together by; suitable wires or conductors so that all. are necessarilyat the same potential.

While the: valve envelope. will. generally be. of glass, the samermethod of construction could. be applied. toquartz and other like. materials workable after softening or melting by heat. Such materials will for convenience be called fusible materials.

What is claimed is:

l. A thermionic valve rectifier comprising an envelope enclosing a plurality of electron emissive cathodes insulated from one another, a plurality of corresponding anodes, and connecting means coupled with said anodes within said envelope to connect said anodes together directly at the same potential.

2. A thermionic valve rectifier comprising an envelope of fusible material, a metallic anode sealed through the said envelope, and a plurality of electron emissive cathodes insulated from one another enclosed in the said envelope, all of the said cathodes being disposed adjacent to corresponding portions of said anode to supply electrons to the said anode when they are appropriately heated and polarised.

3. A thermionic valve rectifier comprising an envelope of fusible material, a metal anode disc sealed through the said envelope dividing it into two compartments, a plurality of electron emissive cathodes enclosed by one of the said compartments and disposed adjacent to corresponding portions of said disc to contribute electrons to the said anode disc when they are appropriately heated and polarised, and a getter holder enclosed in the other compartment.

4. A rectifier according to claim 2 further comprising screen means positioned between adjacent cathodes for preventing the transfer of electrons from one cathode to another.

5. A rectifier according to claim 2 further comprising a metal screen interposed between adjacent cathodes mounted on and electrically con nected to the said anode.

6. A rectifier according to claim 3 comprising two cathodes both enclosed in one of the said compartments.

7. A rectifier according to claim 2 further comprising a metal can enclosing the valve, and means for attaching the said anode disc to the can in good thermal contact therewith.

8. A rectifier according to claim 2 further comprising a metal can enclosing said valve, insulation means interposed between said can and said disc cooperating with said can and said disc for attaching said can to said disc.

9. A rectifier according to claim 2 further comprising a metal can having cooling fins and onclosing said valve, and means cooperating with said can and said disc for attaching said can to said disc.

10. A thermionic valve rectifier comprising an envelope of fusible material, a metal anode disc sealed through the said envelope dividing it into two compartments, a plurality of electron emisslve cathodes enclosed in one of said compartments, all of said cathodes being disposed adjacent to corresponding portions of said disc to supply electrons to the said anode when they are appropriately heated and polarized.

' 11. A thermionic valve rectifier comprising an envelope of fusible material, a metallic anode sealed through said envelope, a plurality of elec tron emissive cathodes insulated from one another enclosed in said envelope, all of said cath- 'odes being disposed adjacent to corresponding portions of said anode to supply electrons to said anode when they are appropriately heated and polarized, and cooling means external to said envelope and thermally coupled to said anode.

CHARLES NORMAN SMYTH.

8 REFERENCES CITED The following references are of record in the file of this patent:

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